DE3331570A1 - METHOD FOR CONTROLLING THE SIZE OF THE PEARLS IN THE PRODUCTION OF EXPANDABLE STYRENE POLYMERISATES BY SUSPENSION POLYMERISATION - Google Patents

Description

CHEMISCHE WERKE HÜLS AG - € - OZ 3933

Process for controlling the size of the beads in the manufacture of expandable styrene polymers by suspension polymerization

Expandable or foamable styrene polymers are essentially by the process of so-called bead polymerization or suspension polymerization obtained in the aqueous phase. The suspension stabilizers used today are usually water-soluble uses organic polymers called protective colloids. Finely divided powders such as B. Calcium or barium sulfate or calcium phosphate can used to stabilize the suspension

10 become. Such stabilizer systems are called

Pickering stabilizers called. A list of technically used protective colloids is z. B. in the article by Trommsdorf and Münster in "Schildknecht": Polymer Processes Vol. 29, pages 119 to 120

15 to find.

The choice of suitable protective colloids is of great importance for the following reasons:

20 1. Setting of narrow particle size distributions with a defined size

Foamable styrofoam polymers are made depending on the size of the beads Various uses: Coarse pearls (2.5 to 0.8 mm) are used for manufacturing 5 of insulating plates are used, finer fractions (0.8 to 0.4 mm in diameter) are used for production used by packaging material. It is therefore necessary that pearls are in the desired grain size range in sufficient quantity, d. i.e., in high yield. The seizure should start Oversized or undersized grains should be as small as possible.

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2. Low internal water content of the pearls

In the usual suspension polymerization, as is known, a certain amount of water is always in the Pearls included. Have polymers with a low content of trapped water in the foamed state has a uniform foam structure, which enhances the thermal insulation properties of the Foam panels positively influenced. One possible low content of trapped water (indoor water) is therefore to be aimed for.

3. Spherical shape of the pearls

In the suspension polymerization of blowing agent-free styrene, because of the better processability, aimed at deformed pearls. In the production of expandable styrene polymers should however, the pearls are as spherical as possible.

4. Sufficient stability of the suspension over the entire polymerization cycle The suspension for the production of expandable styrene polymers is even more unstable than that of blowing agent-free styrene polymers. With today

2 5 usual reactor sizes up to 100 m is the

Loss of an approach therefore constitutes considerable damage. It must therefore be ensured that in the event of accidents the phase separation is so slow that there is enough time, a polymerization inhibitor to add.

None of the suspension systems known to date meet all of these requirements at the same time.

While there has been no lack of attempts to find a feasible 5 way to meet all four requirements at the same time to meet. However, as the known art shows, the efforts have not been successful.

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DE-A-25 48 524 describes a process according to which suspension stabilizers are used, which were produced by radical polymerization of styrene in the presence of polyvinylpyrrolidone. 5

DE - B 2 - 25 10 937 describes a method in which the system is initially in the low viscosity state is weakly stabilized with tricalcium phosphate, a few hours later it is stabilized with a aqueous solution of polyvinylpyrrolidone.

Both processes should be able to produce styrene polymers with a low internal water content. These Processes have the disadvantage, however, that the particle size of the polymer depends on the time at which the organic polymer is added Protective colloid is determined.

The exact determination of the polymerization conversion in the case of heterogeneous batches, as is the case with suspension polymerization is difficult. A precise knowledge of the turnover is necessary for the reproducible setting the particle size spectrum is necessary because the pearl size depends on the viscosity of the polymerizing phase depends at which the protective colloid is added.

5 Besides, the polymerizing system is about 2 hours in an unsafe operating state, which is particularly disadvantageous when using large reactors. An incident, e.g. B. a stirrer failure, especially at the beginning of the polymerization, when the main amount of If styrene is still present, the reactor will be destroyed.

DE-B-20 49 291 proposes two protective colloids, namely polyvinyl alcohol with different Degree of hydroxylation, to be used in order to obtain round beads of uniform size. As the The examples given must show the ratio

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chosen from styrene to water so unfavorably that the process is uneconomical. The process cannot help to specifically control the grain size of the pearls.
5

As already mentioned at the beginning, water-insoluble inorganic powders are also used as suspension stabilizers used. The use of calcium phosphates is the most common. These inorganic compounds are usually used in combination with smaller amounts used on emulsifiers or surfactants (Houben-Weyl, Methods of Organic Chemistry, 4th Edition, Volume XIV, Part 1, Macromolecular Substances, page 425). The application compared to organic protective colloids, however, this system is limited because it is reproducible Handling and a trouble-free course of the suspension polymerization only in a narrow area is possible. On page 422, last paragraph, lines 6 to 8 of this reference is listed:

"It is hardly possible to specify conditions under which a powdery dispersant is a broader Application would be capable ". When combining inorganic compounds with surfactants, the optimal Dosage must be adhered to exactly, as both under-

2 5 dosing as well as overdosing the surfactant can result in coagulation of the batch.

From French patent specification 20 79 991 it is also known, both through the amount of the suspending agent (Protective colloids) or by varying the phase ratio of aqueous to organic phase or by Using a mixture of organic protective colloid and inorganic suspension stabilizer the shape of the Altering pearls. After doing this procedure, you don't necessarily get spherical beads, either no pearls with a low internal water content because the suspending agent is not prior to polymerization

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aqueous phase is added. When adding the suspending agent At the beginning of the polymerization, the grain size cannot be set in a reproducible manner.

The similar process of US Pat. No. 3,222,343 does not meet the required conditions either.

The invention is based on the object of a method for grain size control in suspension polymerization of styrene in which the suspension is stable over the entire polymerization cycle, expandable pearls with low internal water content and spherical shape gives fine and if desired or coarse pearl fractions within the grain size of

15 supplies 0.41 to 2.5 mm in high yield.

According to the invention, this object is achieved by the method laid down in the patent claims.

The following measures are therefore necessary for success: The protective colloids used are before the start of the Polymerization of the aqueous phase added. You must cover the entire temperature range of 2 5 be homogeneously soluble and effective in water up to 125 C. 5 They are used in such a concentration range that that their addition does not lower the interfacial tension water / styrene below 18 N / mm. The styrene / water interfacial tension is 32

2
N./mm. Finally, the weight ratio of the aqueous to the organic phase may only be more than 0.9: 1; in other words in the range 1: 0.9 to 1: 1.25. The organic protective colloids are selected according to their molecular weight. According to the knowledge of the

35 State of the art not to be expected.

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Surprisingly, it turned out that that higher molecular protective colloids result in a finer grain spectrum than lower molecular substances of the same macromolecular compound. Particularly surprising was the effect that even when used low molecular weight protective colloids only the desired, round spherical pearl shape is obtained.

From the article by Winslow and Matreyek (Ind. Engng.

Chem. 43 (1951), page 1108) shows that when using polyvinyl alcohol as a protective colloid the molecular weight only plays a subordinate role compared to the degree of hydroxylation. H. Wennig contributes his investigations "On the colloid chemistry of pearl polymerization" (Kunststoffe-Plastics j> (1958), pages to 340) on page 330 states that the molecular weight of the protective colloid "neither for the interface activity, nor for the emulsification process nor for stability of the emulsion is important ".

Hydroxyethyl cellulose is preferred for the process according to the invention and polyvinylpyrrolidone used as protective colloids because of these Substances are readily available commercially in fractions graded according to molecular weight. As a measure for the molecular weight either the K value according to Fikentscher (Cellulosechemie 13 (1932), page 58), or the reduced specific viscosity indicated. They are used in concentrations between 0.01 to 0.3 Percentage by weight, based on the amount of water used, in particular in concentrations of 0.05 to 0.15 percent by weight, used. They are also in the specified concentration range for the polymerization process prevailing temperatures between

25 ⁰ C and 12 5 ° C clear and completely soluble in water. The interfacial tension between styrene and water is not reduced by the addition of the protective colloid

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lower than 18 N / mm.

Since the commercially available types of protective colloids, graded according to the molecular weight, do not have a uniform molecular weight, but have a molecular weight distribution, it is advantageous for improved grain size control than to add an inorganic powder that is sparingly soluble in water to the second component. On this finely divided Powders are preferably adsorbed high molecular weight fractions of the organic protective colloid, so that for Suspension stabilization only the desired molecular weight fraction is effective. As a useful adsorbent can e.g. B. finely divided tricalcium phosphate or barium phosphate can be used. The weight ratio of organic protective colloid and inorganic fulver is between 1: 1 and 1: 5, in particular between 1: 2 and 1: 4.

The organic protective colloids are used together with the other components of the stabilization system before the start added to the polymerization in the aqueous phase. The water should have an electrical conductivity of less than 0.5 / us (microsiemens). While stirring is the organic phase was added and then heated to -5. The system is therefore at all times the Polymerization sufficiently stable. Should the stirrer fail, the aqueous and organic separation occurs Phase so slowly that there is enough time to add a polymerization inhibitor. It arise Styrofoam polymers, the internal water content of which is extraordinary is low. It is between 0.3 and 1.0 percent by weight.

The setting of the desired particle size spectrum can be 5 either by using defined molecular weight

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fractions of the organic protective colloids alone or by mixing and using the mixture of fractions take place. The concentration should always be chosen so high that there is sufficient stability of the suspension is guaranteed during the entire course of the polymerization. The relationship between aqueous and organic As already mentioned, phase is in the range from 0.9: 1 to 1: 1.25, preferably around 1: 1, however not less than 1: 1.

10

Starting materials for the manufacture of expandable Styrene polymers are styrene and monomer mixtures which contain at least 50 percent by weight of styrene and additionally a monomer which can be copolymerized with styrene,

z. B. X-methylstyrene, p-methylstyrene, nuclear halogenated Styrenes, acrylonitrile, esters of acrylic or methacrylic acid of alcohols with 1 to 8 carbon atoms, N-vinyl compounds, such as N-vinylcarbazole or smaller amounts Contain butadiene or divinylbenzene.

20th

The polymerization is carried out according to the per se known bead polymerization process carried out at temperatures of 80 to 125 ° C. It is used in the usual way initiated one or more radical-forming substances, the usual amounts of 0.2 to 1.0, in particular 0.3 to 0.6 percent by weight, based on the organic phase, are used: t-butyl perbenzoate, t-butyl perisononanate, Di-t-butyl peroxide, dibenzoyl peroxide or mixtures thereof may be mentioned as examples. The styrene polymers can also contain organic halogen compounds as flame retardants, such as the brominated oligomers of butadiene or isoprene. Its typical representatives are: 1,2,5,6-tetrabromocyclododecane, 1, 2, 5, 6, 9,10-hexabromocyclododecane, brominated polybutadiene, with a degree of polymerization of e.g. B. 3 to 15, l - (\ ', ß-dibromoethyl) -3,4-dibromocyclohexane. It can be beneficial

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be, synergistic substances, such as di-t-butyl peroxide, Add poly-p-diisopropylbenzene.

Liquid or gaseous organic compounds are used as propellants for the process according to the invention, which do not dissolve the styrofoam polymer and whose boiling point is below the softening point of the polymer lies, e.g. B. aliphatic hydrocarbons, such as propane, butane, pentane, hexane, cyclohexane or halogenated hydrocarbons, such as methyl chloride, dichloride difluoromethane, trichloromonofluoromethane or 1,2,2-trifluoro-, 1,1,2-trichloroethane. Also mixtures of propellants can be used. The propellants are usually used in amounts of from 2 to 20 percent by weight, preferably 3 to 12 percent by weight, based on the monomers, used.

The expandable styrene polymers can also contain additives such as dyes, fillers and regulating agents for foam porosity, such as epoxy alkanes. The expandable styrene polymers lie after preparation in spherical shape, and generally have a particle diameter of 0.3 to 3 mm, preferably 0.4 to 2.5 mm. They can be pre-expanded in the usual way by heating them in molds, which do not close gas-tight, are further foamed and sintered to form foam moldings that are in their dimensions correspond to the inner cavity of the mold used .

1. Examples : 1.1. Polymerization

The premixed mixtures of organic protective colloid and finely divided tricalcium phosphate are dispersed in 100 parts by weight of deionized water in a stirred tank. Of the

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100 parts by weight of styrene, in which 0.30 part of dibenzoyl peroxide and 0.15 part of t-butyl perbenzoate are dissolved, are added to the dispersion with stirring. This mixture is polymerized for 4 hours at 90 ⁰ C and 6 hours at 115 ° C with stirring. 3 hours after reaching 90 ° C., 7 parts by weight of a mixture of normal and isopentane are added as a propellant. After the end of the polymerization, the stirred tank is emptied and the polymer particles are largely freed from the outside water.

1.2. The internal water is determined as follows: A sample of the expandable polystyrene is used for 2 minutes to remove traces of outside water Treated methanol, then sucked off on a suction filter and 5 minutes with air at 20 ° C blow. The sample prepared in this way is then titrated according to the "Karl Fischer" method.

1.3. Determination of the molecular weight of the protective colloid:

In a 100 ml measuring jar? becomes a solution of the protective colloid made in water at a concentration of 0.002 g / cm. This solution comes in a Capillary viscometer measured and compared with the solvent. From the lead times through the In the capillary, the specific viscosity is determined and from this the reduced based on the concentration specific viscosity or the I-value calculated. The following definitions apply to the value I (g / ml) in the table:

-RED '-RED -SPEZ / c, "SPEZ to

c = 0.002 g / cm = concentration

t = transit time of the solution ) through the

to = throughput time of the!> pillar viscous

Solvent j meter at 25 ° C

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Table 1

Grain size control with hydroxyethyl cellulose batches of different molecular weights

HEC

ι ι

At- ^! lot
play parts by weight / no., 100 parts by weight

I (g / ml)

water

lot

TCP teaspoon by weight / 100 teaspoons by weight of water

Interior Wt%

Grain spectrum % mm
> 2.5! 2.0? 1.12 I 0.9 | 0.63

4-

0.4lk0.41

E 1

V 1

V 2

0.12
0, IO
0.14

675

0.25 0.25 0.25

0.83 0.71 1.12 ^ 479 4, 3 ^ 32, 3 ^ 4X75 14, 5 ^ 572 1.4 ^! 0.8 81.6 18.3 41.4 32.6 4.2 2.4 1.0 0.1 84.3 0.2 2.4 10.7 18.6 34.1 18.5 15, 5

E. 2 0, 15th 485 0, 30th 0, 56 98 9 0 ,1 1, 4th 21 4th 38, 5 27 2 10, 4th 1, 0 V 3 0, 12th 485 0, 30th 0, 76 75 2 24 .2 38, 5 18 7th 10, 5 5, 7th 1, 8th 0, 6th V 4th 0, 17th 485 0, 30th 0, 88 83, 9 - 2, 7th 10, 4th 28, 3 22 4th 20, 1 16, 1

E. 3 0, 22nd 170 0, 35 0, 44 98 0 V 5 0, 20th 170 0, 35 0, 51 81 7th V 6th O, 25th 170 0, 35 0, 72 84, 7th

1.4 10.5 50.7 35.4 2.0

2.2 12.4 17.4 28.5 21.2 18.3

2.3. 18.7 35.3 28.4 15.3

CO GO GO

'' Weight percent in the desired grain size range from 0.41 to 2.5 mm. HEC = hydroxyethyl cellulose, TCP = tricalcium phosphate

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The results compiled in Table 1 show that, depending on the desired range of the particle size spectrum, a certain molecular weight (expressed by the specific viscosity) of the protective colloid leads to an optimal yield in the desired particle size range. The comparative examples show that when a protective colloid with a certain molecular weight is used and the concentration is changed, the yield of usable material in the grain size range between 2.5 and 0.41 mm is negatively influenced. The fines obtained in the comparative tests V 2, V 4 and V 6 cannot be returned as redissolving material, since the adhering amounts of suspending agent are difficult to separate and thus interfere with the subsequent batch. In the comparative experiments V 1, V 3 and V 5, the beads y 1.25 mm are out of round (flat disks), so that the useful yield is actually only 40.2, 36.7 and 79.5 % .

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Tabel

Use of polyvinylpyrrolidone batches of different molecular weights

PVP ⁺ .-TL / ) Molecular weight lot the end > 2.5 Grain size% mm at lot Gew-i K value TCP prey 2.0 1.12! 0.9 0.63 j 0.41 Vo, 41 game Weight What- TL / % ⁺⁺⁾ No. 100 100 wt. Tl. Tl. What ser ser

E. 4th 0, 10 90 0, 10 99 8th 0 .2 V 7th 0, 11 90 0, IO 86 0 - V 8th 0, 09 90 0, 10 80, 2 19th , 4

10.4 48.5 37.5 2.4 1.0

4.5 8.2 22.5 27.4 23.4 14.0
48.7 24.5 3.1 2.3 1.6 0.4

E. 5 0, 15th 30th 0, 15th 98 2 1 - 6th - 4, 4th 24, b 40, 5 28, 7th 1, 8th V 9 0, 16 30th 0, 15th 81 6th - - - 2, 7th 34, 2 44, 7th 18 4th V 10 O, 13th 30th 0, 15th 88 8th , 2 , 4 8th, 5 27 3 28, 5 18 2 9, 9

20 PVP = polyvinylpyrrolidone

⁺⁺ ' Weight percent in the desired grain size range from 0.41 to 2.5 mm

GO CO CO

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10

20th

The fine fraction of the comparative experiments V 7 and V 9 cannot be reused analogously to Table 1; in the comparative experiments V 8 and V 10, non-round beads also occur from a grain size of 1.25 mm, so that the useful yield is 60.8 and 82 mm, respectively , 4 % . A simple method for fine-tuning the particle size spectrum results from the use of mixtures of different molecular weight fractions. This is illustrated by the examples in the following table:
Table 3

Use of mixtures of different molecular weight fractions of hydroxyethyl cellulose (HEC) for grain size control

at total -Tl./ HEC 1 lot -Tl. I. HEC 2 lot I. the end Interior > 2 , 5 2 , 0 Kornspect rum 12th 0.9 I. 4.8 0, % mm <0 , 41 game amount of HEC Weight Weight g / ml Parts by weight g / ml prey Wt .-? I 1, 16.5 63 ¹ 0.4L No. Weight What- · 100 wt % * 48.5 100 Tl. What 18.4 Tl. 12th 09 ser ser 12th 0, 03 67 5 0.03 485 0.72 1 .2 74 , 6 , 5 0 E 6 " 0, 27 0, 17th 67 5 0.09 485 98.8 0.68 0 ,1 48 , 2 18th , 5 2 , 9 0.2 - E 7 0, 22nd 0, 08 48 5 0.10 170 99.9 0.45 - - 32 .2 39 , 5 3.3 0, 8th E 8 0, 0, 485 0.14 170 99.2 0.38 - - 8th ,1 54 , 2 26.8 O, 2 E 9 0, 99.8 0 , 5

Tricalcium phosphate in all examples 0.3% by weight, based on the aqueous phase Weight percent in the desired grain size range 0.41 to 2.5 mm

CO CO CO

cn -J CD

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The advantageous use of mixtures of protective colloids with different molecular weights can be clearly seen from these experiments. In all cases, the yield of beads that can be used is almost ICX %. In addition, the grain size distributions are narrower, i. That is, a desired grain size can be set in a more targeted manner. The internal moisture levels of the products are in all cases below 1 % and are therefore satisfactory.

With the following experiments the different speed the phase separation of the polymerization batch can be demonstrated with the stirrer stopped, depending on whether or not suspending agents are present. In the event of a fault, e.g. B. failure of the stirrer due to gear damage must there is enough time left to add a polymerization stopper to the system prior to phase separation.

For this purpose, 5 kg of deionized water were placed in a 15 l glass flask and 5 kg of styrene (in which the amounts of peroxides specified in Example 1 were dissolved) were added with stirring. After heating to 90 ^° C., polymerization was carried out at this temperature for 30 minutes. The stirrer was then switched off and the time taken for the phases to separate was determined. The batch was then discarded. In 3 experiments, the work was carried out once without a suspension stabilizer, once by the method as described in DE-A-25 10 937 (prepolymerization with addition of calcium phosphate) and finally by the method of the invention.

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Table 4

Duration of the phase separation at Rührerausfall after 30 minutes polymerization at 90 ⁰ C

Protective colloid
in the aqueous
phase

according to

Duration of the phase separation in minutes

without
Tricalcium- DE-OS 25 10 937 phosphate (TCP)

Hydroxiethyl cellulose + TCP according to the invention

Polyvinyl pyrrolidone + TCP according to the invention

1 5

28 30

Only with the method of the invention is there enough time to add a polymerization stopper in an emergency.

Claims (4)

Patent claims: (1.j method of controlling the size of the pearls in the Production of expandable styrene polymers by polymerizing styrene alone or in Mixture with comonomers in aqueous suspension in the presence of organic protective colloids and radical-forming initiators and blowing agents, characterized in that such organic protective colloids are first dissolved in the aqueous phase, which are in the range of 25 to 125 C are homogeneously soluble therein, the concentration range being chosen so that the Interfacial tension between the aqueous phase 15 and the subsequently added organic (Styrenic) phase, which contains the initiator, 2
is not lowered below 18 N / mm and the organic protective colloid has an associated higher or lower narrow molecular weight range, the ratio of aqueous phase to organic phase is above 0.9: 1 and the mixture produced in this way is polymerized in the usual way. 2. The method according to claim 1, 25 characterized in that an inorganic protective colloid which is insoluble in water is also used. 3. Process according to claims 1 and 2, 30 characterized in that HydroxiethyIcellulose as an organic protective colloid or polyvinylpyrrolidone is used. 4. Process according to claims 1 to 3, 35 characterized in that tricalcium phosphate is used as the water-insoluble inorganic protective colloid. - 2 - O.Z. 3933 Process according to claims 1 to 4, characterized in that known flair-inhibiting compounds are also used will. Use of the styrene polymers obtained according to Claims 1 to 5 for the production of foam moldings